Lennox 80UHG2-45, 80UHG2X-60, 80UHG2X-45, 80UHG3-60, 80UHG3X-60 Unit Information

Corp. 9728−L12

Service Literature

80UHG series units are mid−efficiency gas furnaces used
for upflow or horizontal applications only, manufactured
with tubular heat exchangers formed of aluminized steel.
80UHG units are available in heating capacities of 45,000
to 120,000 Btuh and cooling applications up to 5 tons. Refer
to Engineering Handbook for proper sizing.

Units are factory equipped for use with natural gas. Kits are
available for conversion to LPG operation. 80UHG−1 model
units use electronic (direct spark) ignition. 80UHG−2 and −3
model units are equipped with the Lennox SureLight silicon
nitride ignition system. The 80UHGX unit meets the Califor­nia Nitrogen Oxides (NOx) Standards and California Sea­sonal Efficiency requirements. All units use a redundant gas
valve to assure safety shut−off as required by A.G.A. or
C.G.A. Units may be installed in upflow or horizontal position.

All specifications in this manual are subject to change. Pro­cedures outlined in this manual are presented as a recom­mendation only and do not supersede or replace local or
state codes. In the absence of local or state codes, the
guidelines and procedures outlined in this manual (except
where noted) are recommended only and do not constitute
code.

Revised 01−2002

80UHG

TABLE OF CONTENTS

Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Specifications 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Blower Data 3−4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

High Altitude 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Parts Identification 5−6. . . . . . . . . . . . . . . . . . . . . . . . . . . .

I Unit Components 6−15. . . . . . . . . . . . . . . . . . . . . . . . . . .

II Installation 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

III Start Up 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

IV Heating System Service Checks 16−17. . . . . . . . . . .

V Typical Operating Characteristics 18. . . . . . . . . . . . . .

VI Maintenance 19−20. . . . . . . . . . . . . . . . . . . . . . . . . . . .

VII Wiring and Sequence of Operation 21−28. . . . . . . . .

VIII SureLight Troubleshooting Guide 29−34. . . . . . . . . .

Page 1

© 1999 Lennox Industries Inc.

Litho U.S.A.

SPECIFICATIONS

Blower wheel nominal

g

Nominal cooling

)

Up−Flow/Horizontal Filter and Filter Rack Kits

Single (32J02) Te n Pack (66K64)

Blower wheel nominal

g

Nominal cooling

)

Up−Flow/Horizontal Filter and Filter Rack Kits

Single (46J14) Te n Pack (66K65)

Model No. 80UHG2(X)-45 80UHG2(X)-60 80UHG3(X)-60 80UHG2(X)-75 80UHG3(X)-75 80UHG4(X)-75

Input Btuh (kW) 45,000 (13.2) 60,000 (17.6) 75,000 (22.0)

Output Btuh (kW) 36,900 (10.8) 49,200 (14.4) 61,700 (18.1) 61,700 (18.1)

A.F.U.E. 80.1% 80.5% 80.1% 80.0%

California Seasonal Efficiency 75.4% 76.4% 75.9% 76.8% 76.8% 76.3%

Flue size connection diameter  in. (mm) round 3 (76) 4 (102)

Temperature rise range  _F (_C) 30 - 60 (17 - 33) 45 - 75 (25 - 42)

High static cert. by A.G.A./C.G.A.  in wg. (Pa) .50 (125)

Gas Piping Size I.P.S. Natural or LPG/propane 1/2 (13)

Blower wheel nominal

diameter x width

Blower motor output  hp (W) 1/4 (187) 1/3 (224) 1/4 (187) 1/3 (224) 1/2 (373)

Nominal coolin

that can be added

Shipping weight  lbs. (kg) 1 package 130 (59) 135 (61) 140 (64)

Electrical Characteristics 120 volts  60 hertz  1 phase (less than 12 amps) All models

LPG/propane kit LB-69845L (38K84)

Twinning Kit 15L38 − 11lbs. (5 kg)

Up−Flow/Horizontal Filter and Filter Rack Kits Single (32J02) Ten Pack (66K64
No. & sizeoffilters− in. (mm)

Sidewall Power Venting Kit 79J15  25 lbs. (11 kg)

Hanging Bracket Kit LB-69957 (46J66)  15 lbs. (8 kg)

in. 9 x 7 10 x 7 9 x 7 10 x 7 12 x 8

mm 229 x 178 254 x 178 229 x 178 254 x 178 305 x 203

Tons 1, 1-1/2 or 2 2, 2-1/2 or 3 1, 1-1/2 or 2 2, 2-1/2 or 3

kW 3.5, 5.3 or 7.0 7.0, 8.8 or 10.6 3.5, 5.3 or7.0 7.0, 8.8 or 10.6

Optional Accessories (Must Be Ordered Extra)

(1) 16 x 20 x 1 (406 x 508 x 25)

2, 2-1/2, 3,

3-1/2 or 4

7.0, 8.8, 10.6,

12.3 or 14.1

SPECIFICATIONS

Model No. 80UHG3/4(X)-100 80UHG4/5(X)-100 80UHG3/4(X)-120 80UHG4/5(X)-120

Input Btuh (kW) 100,000 (29.3) 120,000 (35.2)

Output Btuh (kW)

A.F.U.E. 80.1% 80.0% 80.0% 80.1%

California Seasonal Efficiency 76.5% 77.0% Not Available 75.5%

Flue size connection diameter  in. (mm) round 4 (102)

Temperature rise range  _F (_C) 45 - 75 (25 - 42) 35 - 65 (19 - 36) 45 - 75 (25 - 42)

High static certified by A.G.A./C.G.A.  in wg. (Pa) .50 (125) .65 (162) .50 (125)

Gas Piping Size I.P.S. Natural or LPG/propane 1/2 (13)

Blower wheel nominal

diameter x width

Blower motor output  hp (W) 1/2 (373) 3/4 (560) 1/2 (373) 3/4 (560)

Nominal coolin

that can be added

Shipping weight  lbs. (kg) 1 package 175 (79)

Electrical Characteristics 120 volts  60 hertz  1 phase (less than 12 amps) All models

LPG/propane kit LB-69845K (81J14)

Twinning Kit 15L38 (5 kg)

Up−Flow/Horizontal Filter and Filter Rack Kits Single (46J14) Ten Pack (66K65
No. & sizeoffilters− in. (mm)

Sidewall Power Venting Kit 79J15  25 lbs. (11 kg)

Hanging Bracket Kit LB-69957 (46J66)  15 lbs. (8 kg)

Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.
Polyurethane frame type filter is furnished with kit.

in. 12 x 8 12 x 9 12 x 8 12 x 9

mm 305 x 203 305 x 229 305 x 203 305 x 229

Tons 2, 2-1/2, 3, 3-1/2 or 4 3-1/2, 4, 5 or 6 2, 2-1/2, 3, 3-1/2 or 4 3-1/2, 4, 5 or 6

kW 7.0, 8.8, 10.6, 12.3 or 14.1 12.3, 14.1, 17.6 or 21.1 7.0, 8.8, 10.6, 12.3 or 14.1 12.3, 14.1, 17.6or21.1

Optional Accessories (Must Be Ordered Extra)

82,000 (24.0)

(1) 20 x 20 x 1 (508 x 508 x 25)

98,400 (28.8)

Page 2

BLOWER DATA

External Static

External Static

External Static

80UHG2−45, 80UHG2−60 AND 80UHG2−75 BLOWER PERFORMANCE

External Static

Pressure

in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s

0 0 1270 600 980 460 770 365 570 270

.05 12 1245 590 975 460 770 365 565 265

.10 25 1220 575 975 460 770 365 565 265

.15 37 1195 565 965 455 765 360 560 265

.20 50 1170 550 960 455 760 360 560 265

.25 62 1140 540 950 450 760 360 555 260

.30 75 1110 525 940 445 760 360 550 260

.40 100 1060 500 910 430 750 355 545 255

.50 125 990 465 880 415 740 350 540 255

.60 150 900 425 810 380 690 325 530 250

.70 175 800 380 740 350 630 295 520 245

NOTE  All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table

High Medium-High Medium-Low Low

Air Volume at Various Blower Speeds

80UHG3−60 AND 80UHG3−75 BLOWER PERFORMANCE

External Static

Pressure

in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s

0 0 1425 670 1240 585 1000 470 800 380

.05 12 1415 670 1230 580 995 470 800 380

.10 25 1400 660 1220 575 990 465 795 375

.15 37 1385 655 1200 565 985 465 795 375

.20 50 1370 645 1180 555 980 460 790 375

.25 62 1350 635 1160 545 970 460 780 370

.30 75 1330 630 1140 540 955 450 770 365

.40 100 1280 605 1095 515 925 435 750 355

.50 125 1210 570 1040 490 900 425 720 340

.60 150 1135 535 985 465 860 405 680 320

.70 175 1070 505 920 435 800 380 630 300

NOTE  All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table

High Medium-High Medium-Low Low

Air Volume at Various Blower Speeds

80UHG4−75, 80UHG3/4−100 AND 80UHG3/4−120 BLOWER PERFORMANCE

External Static

Pressure

in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s cfm L/s

0 0 1830 865 1600 755 1325 625 1070 505 880 415

.05 12 1815 855 1585 750 1320 625 1070 505 880 415

.10 25 1800 850 1570 740 1315 620 1070 505 880 415

.15 37 1875 885 1550 730 1310 620 1065 505 875 415

.20 50 1750 825 1530 720 1300 615 1060 500 875 415

.25 62 1725 815 1515 715 1290 610 1050 495 870 410

.30 75 1700 800 1500 710 1275 600 1040 490 870 410

.40 100 1650 780 1460 690 1245 590 1020 480 860 405

.50 125 1600 755 1420 670 1210 570 1000 470 840 395

.60 150 1550 730 1380 650 1170 550 980 460 820 385

.70 175 1480 700 1330 630 1130 535 960 455 790 375

NOTE  All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table

High Medium-High Medium Medium-Low Low

Air Volume at Various Blower Speeds

Page 3

BLOWER DATA

External Static

80UHG4/5-100 AND 80UHG4/5-120 BLOWER PERFORMANCE

External Static

Pressure

in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s cfm L/s

0 0 2450 1155 2160 1020 1970 930 1700 800 1500 710

.05 12 2440 1150 2155 1015 1965 925 1695 800 1500 710

.10 25 2430 1145 2150 1015 1960 925 1690 800 1495 705

.15 37 2415 1140 2135 1010 1950 920 1685 795 1495 705

.20 50 2400 1135 2120 1000 1940 915 1680 795 1490 705

.25 62 2380 1125 2105 995 1930 910 1675 790 1480 700

.30 75 2360 111 5 2090 985 1915 905 1670 790 1470 695

.40 100 2310 1090 2050 965 1870 880 1650 780 1440 680

.50 125 2260 1065 2000 945 1810 855 1610 760 1410 665

.60 150 2180 1030 1950 920 1750 825 1560 735 1370 645

.70 175 2100 990 1890 890 1700 800 1520 715 1330 630

NOTE  All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table

High Medium-High Medium Medium-Low Low

Air Volume at Various Blower Speeds

FILTER AIR RESISTANCE

cfm (L/s) in. w.g. (Pa)

0 (0) 0.00 (0)

200 (95) 0.01 (2)

400 (185) 0.03 (7)

600 (280) 0.04 (10)

800 (375) 0.06 (15)

1000 (470) 0.09 (22)

1200 (560) 0.12 (30)

1400 (655) 0.15 (37)

1600 (750) 0.19 (47)

1800 (845) 0.23 (57)

2000 (935) 0.27 (67)

2200 (1030) 0.33 (82)

2400 (1125) 0.38 (95)

2600 (1220) 0.44 (110)

Refer to table below for manifold pressure settings for
Installations at different altitudes and different fuels.

NOTE−In Canada, certification for installations over
4500 ft. (1372m) above sea level is the jurisdictionof
the local authorities.

Manifold Absolute Pressure in. w.c. (kPa)

ALTITUDE ft. (m)

FUEL

NAT 3.5 (0.87) 3.4 (0.85) 3.3 (0.82) 3.2 (0.80)

LP 9.5 (2.36) 9.2 (2.29) 8.9 (2.21) 8.6 (2.14)

0−4500

(0−1372)

4500−5500

(1372−1676)

5500−6500

(1676−1981)

HIGH ALTITUDE DERATE

The combustion air inducer prove switches are factory
set and are not to be adjusted.
At elevations of 4500 ft. (1372m) or greater, change factory
installed pressure switch to switch listed in table below.

6500−7500

(1982−2286)

Page 4

UNIT MODEL

80UHG−45 NO CHANGE

80UHG−60 NO CHANGE

80UHG−75 88J8001

80UHG−100 18L2401

80UHG−120 18L2401

PRESSURE SWITCH

PART NUMBER

80UHG PARTS IDENTIFICATION

FLUE BOX

VENT ADAPTER

HEAT EXCHANGER

ASSEMBLY

CABINET TOP

COMBUSTION AIR

INDUCER

FRONT ACCESS

PANEL

ROLLOUT SWITCH (2)

PROVE

SWITCH

BURNER

ASSEMBLY

TRANSFORMER

CONTROL

BOARD

DOOR INTERLOCK SWITCH

SECONDARY

LIMITS

BLOWER ASSEMBLY

FIGURE 1

HEATING COMPONENTS (shown in horizontal position)

80UHG

CABINET

CABINET

BOTTOM

PRIMARY LIMIT

COMBUSTION AIR

PROVE SWITCH

MANIFOLD

BURNERS

GAS VALVE

COLLECTOR

FIGURE 2

Left

Bottom

Front

Right

HEAT EXCHANGER

COMBUSTION AIR INDUCER

Back

To p

Page 5

80UHG BURNER ASSEMBLY (shown in upflow position)

−2 MODEL SHOWN

SURELIGHT

IGNITOR

BURNER BOX

TOP

UPPER

BURNER

MOUNTING

RAIL

LOWER

BURNER

MOUNTING

RAIL

FLAME

SENSOR

ORIFICE

MANIFOLD

ROLLOUT

SWITCHES

FIGURE 3

I−UNIT COMPONENTS (Figures 1, 2, 3)

80UHG unit components are shown in figure 1. The gas
valve, combustion air inducer and burners can be ac­cessed by removing the burner access panel. Electrical
components are mounted to the blower housing.
80UHG units are factory equipped with bottom return air pan­els in place. The panels are designed to be field removed as

required for bottom air return. Knockout panels are provided
for side return air.

ELECTROSTATIC DISCHARGE (ESD)

Precautions and Procedures

BURNER

VEST PANEL

HEAT EXCHANGER

GAS VALVE

BURNER BOX

PRIMARY LIMIT

Left

Front

To p

Back

Right

Bottom

1− Control Transformer (T1)

A transformer located on the blower housing provides
power to the low voltage section of the unit. Transformers
on all models are rated 30VA with a 120V primary and a
24V secondary.

2−Door Interlock Switch (S51)

A door interlock switch rated 16A at 125VAC is wired in se­ries with line voltage. When the blower door is removed the
unit will shut down.

DANGER

CAUTION

Electrostatic discharge can affect electronic
components. Take precautions during furnace
installation and service to protect the furnace’s
electronic controls. Precautions will help to
avoid control exposure to electrostatic dis­charge by putting the furnace, the control and
the technician at the same electrostatic poten­tial. Neutralize electrostatic charge by touching
hand and all tools on an unpainted unit surface,
such as the gas valve or blower deck, before per­forming any service procedure.

Shock hazard.
Spark related components contain high voltage.

Disconnect power before servicing. Control is
not field repairable. If control is inoperable, sim­ply replace entire control.

Can cause injury or death. Unsafe operation will
result if repair is attempted.

Page 6

3− Furnace Control (A3)

80UHG−2, −3 Models

80UHG−2 and −3 model units are equipped with the Len­nox SureLight ignition system. The system consists of
ignition control board (figure 6 with control terminal desig­nations in table 4) and ignitor (figure 7). The board and ig­nitor work in combination to ensure furnace ignition and
ignitor durability. The SureLight integrated board controls
all major furnace operations. The board also features two
LED lights for troubleshooting and two accessory termi­nals rated at (4) four amps. See table 3 for troubleshoot­ing diagnostic codes. Table 1 and 2 show jack plug termi­nal designations. Units equipped with the SureLight
board can be used with either electronic or electro−me­chanical thermostats without modification. The SureLight
ignitor is made of durable silicon−nitride. Ignitor longevity
is also enhanced by voltage ramping by the control board.
The board finds the lowest ignitor temperature which will
successfully light the burner, thus increasing the life of the
ignitor. Each time power is applied to the furnace, the Sur­eLight board performs a selfcheck including energizing
the combustion air blower for a period of 1 second.

TABLE 1

SureLight BOARD J156 (J2) TERMINAL

PIN # FUNCTION

1 Combustion Air Inducer Line

2

3

4

SureLight BOARD J58 (J1) TERMINAL

PIN # FUNCTION

1 Primary Limit / Pressure Switch Out

2

3

4

5

6

7

8

9

10

11

12

DESIGNATIONS

Ignitor Line

Combustion Air Inducer Neutral

Ignitor Neutral

TABLE 2

DESIGNATIONS

Secondary Limit

24V

Not Used

Rollout Switch In

24V

Primary Limit In

Ground

Gas Valve In

Pressure Switch In

Rollout Switch Out

Gas Valve Out

a−Electronic Ignition (See Figure 5)

On a call for heat the SureLight control monitors the com­bustion air inducer pressure switch. The control will not be­gin the heating cycle if the prove switch is closed (by−
passed). Once the prove switch is determined to be open,
the combustion air inducer is energized. When the differ­ential in the prove switch is great enough, the prove switch
closes and a 15−second pre−purge begins. If the prove
switch is not proven within 2−1/2 minutes, the control goes
into Watchguard−Pressure Switch mode for a 5−minute re−
set period.
After the 15−second pre−purge period, the SureLight igni­tor warms up for 20 seconds during which the gas valve
opens at 19 seconds for a 4−second trial for ignition. The
ignitor stays energized for the first second of the 4−second
trial. 80UHG units equipped with control 10M9301: ignitor
remains energized during the 4 second trial until flame is
sensed. If ignition is not proved during the 4−second peri­od, the control will try four more times with an inter purge
and warm−up time between trials of 35 seconds. After a to­tal of five trials for ignition (including the initial trial), the
control goes into Watchguard−Flame Failure mode. After a
60−minute reset period, the control will begin the ignition
sequence again.
The SureLight control board has an added feature that
prolongs the life of the ignitor. After a successful ignition,
the SureLight control utilizes less power to energize the ig­nitor on successive calls for heat. The control continues to
ramp down the voltage to the ignitor until it finds the lowest
amount of power that will provide a successful ignition.
This amount of power is used for 255 cycles. On the 256th
call for heat, the control will again ramp down until the low­est power is determined and the cycle begins again.

b−Fan Time Control

The fan on time of 45 seconds is not adjustable. Fan off
time (time that the blower operates after the heat demand
has been satisfied) can be adjusted by flipping the dip
switches located on the SureLight integrated control. The
unit is shipped with a factory fan off setting of 90 seconds.
Fan off time will affect comfort and is adjustable to satisfy
individual applications. See figure 4.

FAN-OFF TIME ADJUSTMENT

60sec. 90sec. 120sec. 180sec.

To adjust fan−off timing, flip dip switch to desired setting.

FIGURE 4

Page 7

The SureLight board is equipped with two LED lights for troubleshooting. The diagnostic codes are listed below in table 3.

TABLE 3

DIAGNOSTIC CODES

MAKE SURE TO ID LED’S CORRECTLY: REFER TO INSTALLATION INSTRUCTIONS FOR CONTROL BOARD LAYOUT.

LED #1 LED #2 DESCRIPTION

SIMULTANEOUS

SLOW FLASH

SIMULTANEOUS FAST

FLASH

SLOW FLASH ON

OFF SLOW FLASH

ALTERNATING SLOW

FLASH

SLOW FLASH OFF

ON SLOW FLASH

ON
ON

OFF

FAST FLASH SLOW FLASH

SLOW FLASH FAST FLASH

ALTERNATING FAST

FLASH

SIMULTANEOUS

SLOW FLASH

SIMULTANEOUS FAST

ALTERNATING SLOW

ALTERNATING FAST

FLASH

FLASH

ON

OFF

ON

FLASH

Also signaled during cooling and continues fan.

Normal operation − signaled when heating demand initiated at thermostat.

Primary or Secondary limit open. Units with board 12L69: Limit must close within
5 trials for ignition or board goes into one hour limit Watchguard. Units with board

56L84: Limit must close within 3 minutes or board goes into one hour limit Watch-

Pressure switch open or has opened 5 times during a single call for heat; OR:

Blocked inlet/exhaust vent; OR: Condensate line blocked; OR: Pressure switch

closed prior to activation of combustion air blower.

Flame sensed without gas valve energized.

Rollout switch open. OR: 9 pin connector improperly attached.

Circuit board failure or control wired incorrectly.

Main power polarity reversed. Switch line and neutral.

Low flame signal. Measures below 0.2 microAmps. Replace flame sense rod.

Improper main ground or line voltage below 75 volts; OR: Broken ignitor; OR:

Power − Normal operation

guard.

Watchguard − burners fail to ignite.

Open ignitor circuit.

NOTE − Slow flash equals 1 Hz (one flash per second). Fast flash equals 3 Hz (three flashes per second). Drop out flame sense current < 0.15 microAmps

SureLight Control Ignition Sequence

(Control 56L8401 ONLY)

15

ON

OFF

DEMAND
CA
B

IGNITOR
GAS VALVE
INDOOR BLOWER

*Blower on time will be 45 seconds after ignition. Blower off time will depend on OFF TIME" Setting.

Pre −Purge Ignitor Warmup Trial for

341

35

Ignition

38

Blower On"

Delay

5 SEC80

Post

Purge

FIGURE 5

Page 8

SURELIGHT INTEGRATED CONTROL BOARD

XFMR−N

Flame
sense

COOL−H

TERMINAL DESIGNATIONS

HEAT−H
EAC−H
HUM−H
XFMR−H
LINE−H
LINE−N
HUM−N
EAC−N
XFMR−N
CIR−N

PARK

(FLAME SENSE)

SURELIGHT IGNITOR

TABLE 4

Blower − Cooling Speed (120VAC)
Blower − Heating Speed (120VAC)
Electronic Air Cleaner (120VAC)
Humidifier (120VAC)
Transformer (120VAC)
Input (120VAC)
Input (Neutral)
Humidifier (Neutral)
Electronic Air Cleaner (Neutral)
Transformer (Neutral)
Not Used

SureLight Ignitor

FIGURE 6

4−Flame Sensor 80UHG −2 models

A flame sensor is located on the left side of the burner sup­port. See figure 8. The sensor is mounted on a bracket in
the burner support and the tip protrudes into the flame en­velope of the left−most burner. The sensor is fastened to
burner supports and can be removed for service without
removing any part of the burners. During operation, flame
is sensed by current passed through the flame and sens­ing electrode. The SureLight control allows the gas valve
to remain open as long as flame signal is sensed.

NOTE − The 80UHG furnace contains electronic com­ponents that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.

BURNER

NORMAL FLAME SIGNAL u 0.2 MICROAMPS
LOW FLAME SIGNAL v 0.2 MICROAMPS
MINIMUM FLAME SIGNAL v 0.15 MICROAMPS

1/4 in. 7 mm

 1/32 in. 0.79

mm

3/16 in.

4.7 mm

FLAME

SIDE VIEW END VIEW

SENSOR

11/16 in. 18 mm

 1/32 in. 0.79

FIGURE 8

mm

Page 9

5− Furnace Control (A3) 80UHG−1 Model

80UHG units are equipped with an integrated ignition/blower
control (EGC-2) which controls ignition, safety circuits,
blower operation, fan off timing, and allows for thermostat
connection and troubleshooting. The EGC-2 is a printed
circuit board which is divided into two sections, 120 and
24VAC. Line voltage comes into the board on the 120VAC
side. See figure 10. Terminal designations are listed in
tables 6 and 7.

Ignition Control

80UHG units use the EGC−2 direct spark integrated
ignition control. The EGC−2 controls and monitors the
entire sequence of operation. On a call for heat from the
thermostat the control monitors the combustion air in­ducer prove switch. The control will not begin the heat­ing cycle if the prove switch is closed (by-passed). Once
the prove switch is determined to be open, the combustion
air inducer is energized. When the differential in pressure
across the prove switch is great enough, the prove switch
closes and a 15 second pre-purge period begins. If the
prove switch does not close within 2 1/2 minutes, the con­trol goes into 5 minute watchguard. After the pre-purge pe­riod, the gas valve will open and ignition (spark) will be at­tempted for 10 seconds. After ignition, the control initiates a
ten second flame stabilization period. The flame stabi­lization period allows the burners to heat up and the
flame to stabilize. Once flame is established, the control will
constantly monitor the burner flame using flame rectification.
Flame failure response time is 0.8 seconds.

If the initial attempt for ignition fails, the sequence is re­peated up to five times. After the fifth trial, the control goes into
Watchguard"*. During watchguard mode, the entire unit will
be de-energized for one hour. After one hour the control will
repeat the ignition sequence. Watchguard may be manually
reset by breaking and remaking thermostat demand.

*NOTE−If flame is established beyond the 10 second flame
stabilization period then lost, the control resets for five more
ignition trials. The control can be reset five times during one
unsatisfied thermostat demand, providing a maximum
of 25 trials for ignition.

Safety Circuits

During the entire heating demand the control monitors the
safety circuits. If the primary or secondary heating limits
open, the control de-energizes the main gas valve and
combustion air blower while the indoor blower remains en­ergized. When the limit automatically resets, the ignition se­quence also resets. If either of the limits trip five consecu­tive times during one unsatisfied thermostat demand, the
control will go into watchguard for one hour.

The control monitors main valve voltage. If voltage is sensed

when no voltage should be present, the control de-energizes
the combustion air inducer which terminates voltage to the
valve. The system goes into hard lock-out which is reset only
by removing power to the unit.

If flame is sensed when no flame should be present, the con­trol will energize the combustion and indoor blowers. The
unit will remain locked in this sequence until the flame is no
longer sensed or the main power is turned off to reset the
control.

The roll-out circuit is also monitored by the EGC-2 control. If
the switch opens, the control will de-energize the gas
valve, combustion air inducer, and indoor blower. The
unit will remain de-energized until the switch is manual­ly reset.

DANGER

Shock hazard. Avoid personal injury. Make sure to
disconnect power before changing fan off" timing.

Blower Operation / Fan Off Timings

Fan off" timing (time that the blower operates after the heat
demand has been satisfied) can be adjusted by moving the
jumper on the EGC-2 blower control board. Figure 9 shows
the various fan off" timings and how jumper should be posi­tioned. To adjust fan off " timing, gently disconnect jumper
and reposition across pins corresponding with new timing.
Unit is shipped with a factory fan off" setting of 180 seconds.
Fan on" time is factory set at 45 seconds following the
opening of the main gas valve and is not adjustable.

Fan off" time will affect comfort and efficiency and is ad­justable to satisfy individual applications. The fan off" tim­ing is initiated after a heating demand but not after a cool­ing demand.

NOTEIf fan off" time is set too low, residual heat in
heat exchanger may cause primary limit S10 to trip, re­sulting in frequent cycling of blower. If this occurs, adjust
blower to longer fan off" time setting.

FAN-OFF TIME ADJUSTMENT

TIMING

JUMPER

180

120 90

60

FIGURE 9

To adjust fan-off timing:

Remove jumper from EGC-2 and select

one of the other pin combinations to

achieve the desired time.

TIMING PINS

(seconds)

Leave jumper off for

240 second fan-off timing.

Page 10

Thermostat Connection

Thermostat wires are connected to the terminal strip
found on the EGC-2 control board.

Troubleshooting

The EGC-2 control board is equipped with two diagnostic
green LEDs to indicate the mode of failure. The LED lights
are marked DIAG #1 and DIAG #2. The codes are given in
table 5.

A slotted edge connector is also provided for the Lennox
Diagnostic Module (part number 11K75). See figure 10.
When connected to the EGC-2 control board, the module dis­plays (in words) the diagnostic condition.

80UHG−1 MODEL INTEGRATED CONTROL (EGC−2)

(Shown as installed in horizontal left hand application)

(See tables 6 and 3 for terminal designations)

TABLE 5

EGC-2 DIAGNOSTIC CODES

DIAG #2 DIAG #1 DIagnostic Condition

Simultaneous

Flash

On Flash

Flash Off

Alternate

Flash

Off Flash

Flash On

Continuous

On

Simultaneous

Flash

Alternate Flash

Continuous On

Power ON". Normal Operation. In-

creased flash rate indicates there

is a heating demand.

Primary or Secondary

Limit Switch Open.

Auto-Reset Switch.

Pressure Switch Watchguard,

pressure switch opened during

Circuit board self-check failure or

operation.

Watchguard, burners

failed to ignite.

Flame sensed without

valve energized.

Roll-out Switch Open.
Manual-Reset Switch.

ignition/blower control

is wired incorrectly.

DIAGNOSTIC MODULE

DIAGNOSTIC LEDS

BLOWER TIME

ADJUSTMENT

JUMPER

THERMOSTAT

TERMINAL STRIP

(DETACHABLE)

EDGE

CONNECTION

8 9 10 11 12 13 15

7

6

5

4

1

7

2

8

5

14

PLUG P20

24VAC

346

9

DIAGNOSTIC CODE ERASE JUMPER

(Remove power to control and short pins for

10 seconds to erase previous code.)

FIGURE 10

Page 11

123

TABLE 6

BLOWER CONTROL A15 TERMINAL DESIGNATIONS

Ter mi na l
Designation
(See fig. 10)

R Screw Strip 24VAC to Thermostat (Red)

G Screw Strip

W Screw Strip

Y Screw Strip

C Screw Strip Common Ground to Thermostat

1 1/4" Spade 24VAC Hot from Transformer
2 1/4" Spade 24VAC Return to Transformer
3 1/4" Spade 24VAC Ground

4, 5, 6 1/4" Spade 120VAC Return − 120VAC Common

7 1/4" Spade

8 1/4" Spade Combustion Blower (Line Voltage)

9 1/4" Spade Heat Only Accessory (Line Voltage)
10 1/4" Spade 120VAC Hot to Transformer
11 1/4" Spade 120VAC Hot Input

12, 13 1/4" Spade Accessories (Line Voltage)

14 1/4" Spade ACB Cool Speed (Line Voltage)
15 1/4" Spade ACB Heat Speed (Line Voltage)

Type Function

Manual Fan Input from Thermostat

Heat Demand Input from Thermostat

Cool Demand Input from Thermostat

120VAC Return − 120VAC Common

(Green)

(White)

(Yellow)

Input

TABLE 7

EGC-2 CONTROL JACK/PLUG 20 TERMINAL DESIGNATIONS

Pin # Function

1 Rollout Switch Out
2 Spare
3 Gas Valve Common
4 Pressure Switch Return
5 Hi Limit Return / Pressure Switch Out
6 Flame Sensor
7 Gas Valve Out
8 High Limit Out
9 Rollout Switch Return

6−Blower Motors and Capacitors

All 80UHG units use direct drive blower motors. All motors
used are 120V permanent split capacitor motors to ensure
maximum efficiency. See table 8 for ratings.

80UHG BLOWER RATINGS 120V 1PH

BLOWER MOTOR

80UHG2
80UHG3
80UHG3/4
80UHG4
80UHG4/5
80UHG5/6

TABLE 8

HP
1/4 5MFD 370V
1/3
1/2
1/2 7.5MFD 370V
3/4 40MFD 370V
3/4 40MFD 370V

CAP

5MFD 370V

7.5MFD 370V

SUPPLY AIR BLOWER

AND SECONDARY LIMITS

MOTOR

CAPACITOR

To Remove Blower From Unit: Remove Bolts and

Wiring Jackplugs. Then Slide Out Front of Unit.

SECONDARY

LIMITS (S21)

Left

Front

Bottom

To p

BLOWER

MOTOR

Back

Right

FIGURE 11

7−Combustion Air Inducer (B6)

All 80UHG units use a combustion air inducer to move air
through the burners and heat exchanger during heating
operation. The blower uses a 120VAC motor. The motor
operates during all heating operation and is controlled by
furnace control A3. The blower also operates for 15 sec­onds before burner ignition (pre-purge) and for 5 seconds
after the gas valve closes (post-purge)

A proving switch connected to the combustion air inducer
housing is used to prove combustion air inducer operation.
The switch monitors air pressure in the blower housing. Dur­ing normal operation, the pressure in the housing is nega­tive. If pressure becomes less negative (signifying an ob­struction) the prove switch opens. When the prove switch
opens, the furnace control (A3) immediately closes the gas
valve to prevent burner operation.

8−Flame Rollout Switches (S47)

Flame rollout switch is a high temperature limit located on
top of the burner box. Each furnace is equipped with two
identical switches. One switch is located over the leftmost
burner and the other switch is located over the rightmost
burner. The limit is a N.C. SPST manual-reset limit con­nected in series with the ignition control A3. When S47

Page 12

senses rollout, the ignition control immediately stops igni­tion and closes the gas valve. If unit is running and flame
rollout is detected, the gas valve will close and ignition con­trol will be disabled. Rollout can be caused by a blocked
flue or lack of combustion air. The switch is factory set and
cannot be adjusted. The setpoint will be printed on the side of
the limit. The switch can be manually reset. To manually re­set a tripped switch, push the reset button located on the
control.

ROLLOUT SWITCH (S47)

MANUAL

RESET BUTTON

FIGURE 12

9−Primary Limit Control (S10)

LIMIT CONTROL FOR

80UHG SERIES UNITS

THIS TYPE AUTO-RESET LIMIT

IS USED FOR THE PRIMARY LIMIT (S10) AND

RIGHT SECONDARY LIMIT (S21)

(see FIGURE 11)

FIGURE 13

The primary limit (S10) on 80UHG units is located in the
middle of the heating vestibule panel. When excess heat is
sensed in the heat exchanger, the limit will open. If the limit is
tripped, the furnace control energizes the supply air blower
and closes the gas valve. The limit automatically resets when
unit temperature returns to normal. The switch is factory set
and cannot be adjusted. The switch may have a different
setpoint for each unit model number. However, the setpoint
will be printed on the side of the limit.

10−Secondary Limit Controls (S21)

The secondary limit (S21) on 80UHG units is located in the
blower compartment in the back side of the blower housing.
When excess heat is sensed in the blower compartment, the
limit will open. If the limit is tripped, the furnace control ener­gizes the supply air blower and closes the gas valve. The limit
automatically resets when unit temperature returns to normal.
The switch is factory set and cannot be adjusted. The set­point will be printed on the limit.

Two limits are supplied in each furnace. 80UHG3, 80UHG4
and 80UHG4/5 model units built prior to Apri 1999, will
have one each of style shown in figures 13 and 14. If stick
limit (figure 14) suffers frm nuisance trips on the above
model units and the furnace is in the horizontal position, re­place with limit kit no. 50L98. All 80UHG2 model units will
have one of each style shown in figures 13 and 14.

SECONDARY LIMIT CONTROL (S21)

INSULATING COVER

LIMIT

FOR 80UHG SERIES UNITS

THIS TYPE AUTO-RESET LIMIT IS

SPADE CONNECTORS

USED FOR THE LEFT SECONDARY

LIMIT (S21) (see FIGURE 11)

INSULATING COVER (s)

LIMIT

FIGURE 14

11−Spark Electrode and Flame Sensor

80UHG−1 Models

Figure 17 shows the arrangement of flame sensor, spark
electrode and burners. The ignition control uses direct
spark to ignite the rightmost burner and the burners cross­light to the left. The flame sensor uses flame rectification to
sense combustion. A flame retention ring in the end of
each burner is used to maintain correct flame length and
shape and to keep the flame from lifting off the burner
head.
Figure 18 shows the gap between tip of the electrodes and
the burner surface, and the gap between the sensor and
burner surface.

12−Gas Valve

The 80UHG uses a gas valve manufactured by Honey­well or White Rodgers. The valve is internally redundant to
assure safety shut−off. If the gas valve must be replaced,
the same type valve must be used.
24VAC terminals and gas control knob are located on top of
the valve. All terminals on the gas valve are connected to
wires from the electronic ignition control. 24V applied to the
terminals energizes the valve.
Inlet and outlet pressure taps are located on the valve. A regu­lator adjustment screw (figures 15 and 16) is located on the
valve.
LPG changeover kits are available from Lennox. Kit s include
burner orifices and a gas valve regulator conversion kit.

Page 13

WHITE RODGERS 36E SERIES GAS VALVE

MANIFOLD

PRESSURE

ADJUSTMENT

SCREW

HONEYWELL VR8205 SERIES GAS VALVE

MANIFOLD

PRESSURE

ADJUSTMENT

SCREW

MANIFOLD

PRESSURE

OUTLET

GAS VALVE SHOWN IN OFF POSITION

FIGURE 15

TYPICAL BURNER/ELECTRODE ORIENTATION

1/8"(+1/64")

SPARK ELECTRODE

UPPER BURNER
MOUNTING RAIL

GROUND

SPARK ELECTRODE TO BURNER GAP

80UHG−1 MODEL SHOWN

BURNER

SPARK

ELEC-

TRODE

SPARK ELECTRODE

FLAME SENSOR TO BURNER GAP

BURNER

MANIFOLD

PRESSURE

OUTLET

80UHG−1 MODEL SHOWN

BURNER

FLAME RETENTION RING

FIGURE 17

5/16 in.

(7 mm)

5/16 in.

(7 mm)

ON

OFF

GAS VALVE SHOWN IN OFF POSITION

FIGURE 16

To p

Right Left

Bottom

MANIFOLD ORIFICE

LOWER BURNER

MOUNTING RAIL

23/32 in.
(18 mm)

FLAME SENSOR

13−Combustion Air Blower Prove

Switch (S18)

80UHG series units are equipped with a combustion air
prove switch located on the vestibule panel. The switch is
connected to the combustion air inducer housing by means
of a flexible silicone hose. It monitors air pressure in the
combustion air blower housing.

The switch is a single-pole single-throw pressure switch
electrically connected to the furnace control. The purpose
of the switch is to prevent burner operation if the combus­tion air blower is not operating or if the flue becomes ob­structed.

FLAME SENSOR

FIGURE 18

Page 14

COMBUSTION AIR INDUCER

PROVE SWITCH

Normally Open

Closes on Negative Pressure

Sensing Tube

Attaches to Top

Side Of Blower

To p

PROVE

SWITCH

Back

Left

Right

Front

Bottom

FIGURE 19

On start-up, the switch senses that the combustion air
blower is operating. It closes a circuit to the furnace control
when pressure inside the combustion air blower de­creases to a certain set point. Set points vary depending
on unit size. The pressure sensed by the switch is relative
to atmospheric pressure. If the flue becomes obstructed
during operation, the switch senses a loss of negative
pressure (pressure becomes more equal with atmospher­ic pressure) and opens the circuit to the furnace control
and gas valve. A bleed port on the switch allows dry relativ­ity air in the vestibule to purge switch tubing, to prevent
condensate build up. The switch also has an internal inline
orifice, designed to prevent nuisance shut downs due to
erratic vent pressure fluctuations.
The switch is factory set and is not field adjustable. It is a
safety shut-down control in the furnace and must not be
by−passed for any reason. If switch is closed or by−passed,
the control will not initiate ignition at start up.

II−PLACEMENT AND INSTALLATION

PROVE SWITCH

Make sure unit is installed in accordance with installation
instructions and applicable codes.

III−START-UP
A−Preliminary and Seasonal Checks

1 − Inspect electrical wiring, both field and factory installed

for loose connections. Tighten as required.

2 − Check voltage at disconnect switch. Voltage must be

within range listed on the nameplate. If not, consult the
power company and have voltage condition corrected
before starting unit.

B−Heating Start-Up

WARNING

Shock and burn hazard.

80UHG−1 units are equipped with a direct spark igni­tion system. Do not attempt to light manually.

1 − STOP! Read the safety information at the beginning

of this section.

2 − Set thermostat to lowest setting.
3 − Turn off all electrical power to appliance.
4 − This appliance is equipped with an ignition device

which automatically lights the burners. Do not try to

light the burners by hand.
5 − Remove top access panel.
6 − White Rodgers 36E Gas Valve −− Switch lever to

OFF. See figure 15.

Honeywell VR8205 Gas Valve −− Turn knob on gas

valve clockwise to OFF. Do not force. See fig-

ure 16.
7 − Wait five (5) minutes to clear out any gas. If you then

smell gas, STOP! Close manual main shut−off valve to

the furnace. Immediately call your gas supplier from a

neighbor’s phone. Follow the gas supplier’s instructions.

If you do not smell gas go to next step.
8 − White Rodgers 36E Gas Valve −− Switch gas valve lever

to ON.

Honeywell VR8205 Gas Valve −− Turn knob on gas

valve counterclockwise to ON. Do not force.
9 − Replace access panel.

10− Turn on all electrical power to unit.
11− Set thermostat to desired setting.

NOTE−When unit is initially started, steps 1 through 11
may need to be repeated to purge air from pilot line.

12− If the appliance will not operate, follow the instructions

To Turn Off Gas To Unit".

Turning Off Gas To Unit

1 − Set thermostat to lowest setting.
2 − Turn off all electrical power to unit if service is to be

performed.
3 − Remove access panel.

4 − Switch lever on White Rodgers gas valve to OFF; turn

knob on Honeywell valve clockwise to OFF. Do not

force.
5 − Replace access panel.

C−Safety or Emergency Shutdown

Turn off unit power. Close manual and main gas valves.

D−Extended Period Shutdown

Turn off thermostat or set to UNOCCUPIED" mode. Close
all gas valves (both internal and external to unit) to guaran­tee no gas leak into combustion chamber. Turn off power
to unit. All access panels, covers and vent caps must be in
place and secured.

Page 15

IV−HEATING SYSTEM SERVICE CHECKS

A−A.G.A./C.G.A. Certification

All units are A.G.A. and or C.G.A. design certified without
modifications. Refer to the 80UHG Operation and Installa­tion Instruction Manual Information.

B−Gas Piping

Gas supply piping should not allow more than 0.5"W.C.
drop in pressure between gas meter and unit. Supply gas
pipe must not be smaller than unit gas connection.

Compounds used on gas piping threaded joints should be
resistant to action of liquefied petroleum gases.

C−Testing Gas Piping

IMPORTANT

In case emergency shutdown is required, turn off
the main shut-off valve and disconnect the main
power to unit. These controls should be properly
labeled by the installer.

When pressure testing gas lines, the gas valve must be
disconnected and isolated. Gas valves can be damaged if
subjected to more than 0.5psig (14" W.C.). See figure 20. If
the pressure is equal to or less than 0.5psig (14"W.C.), use
the manual shut−off valve before pressure testing to iso­late furnace from gas supply.

GAS PIPING TEST PROCEDURE

MANUAL MAIN SHUT−OFF VALVE

WILL NOT HOLD TEST PRESSURE

IN EXCESS OF 0.5 PSIG (14"W.C.)

through Lennox under part number 31B2001. See Corp.
8411−L10, for further details.

Do not use matches, candles, flame or any other source of
ignition to check for gas leaks.

D−Testing Gas Supply Pressure

When testing supply gas pressure, connect test gauge to
inlet pressure tap (field provided). See figure 20. Check
gas line pressure with unit firing at maximum rate. Low
pressure may result in erratic operation or underfire. High
pressure can result in permanent damage to gas valve or
overfire. For 80UHG−45,60 and 75 BTUH natural gas
units, operating pressure at the unit must be a minimum

4.5"W.C. For the 80UHG−100 and 120 BTUH units, the op­erating pressure must be a minimum of 5.0"W.C. For L.P.
gas units, operating pressure at unit gas connection must
be a minimum of 11.0" W.C.

On multiple unit installations, each unit should be checked
separately, with and without other units operating. Supply
pressure must fall within range listed in previous para­graph.

E−Check Manifold Pressure

After line pressure has been checked and adjusted, check
manifold pressure. Move pressure gauge to outlet pres­sure tap located on unit gas valve (GV1). Checks of man­ifold pressure are made as verification of proper regulator
adjustment. Manifold pressure for the 80UHG can be mea­sured at any time the gas valve is open and is supplying gas
to the unit. Normal manifold pressure for natural gas units is

3.5 in. W.C. For LP/propane gas the correct manifold pres­sure is 9.5 in. W.C.

IMPORTANT

GAS VALVE

FIELD PROVIDED

LINE PRESSURE

FIGURE 20

When checking piping connections for gas leaks, use pre­ferred means. Kitchen detergents can cause harmful corro­sion on various metals used in gas piping. Use of a specialty
Gas Leak Detector is strongly recommended. It is available

CAP

TAP

Page 16

For safety, connect a shut-off valve between the
manometer and the gas tap to permit shut off of
gas pressure to the manometer.

Unit (Fuel)

GAS VALVE REGULATION

L.P. 9.5 + 0.5

The gas valve is factory set and should not require adjust­ment. All gas valves are factory regulated. See table 9.
See specifications section of this manual for High Altitude
manifold pressure settings.

TABLE 9

Operating Pressure (outlet) in. W.C.

3.5 +0 −0.3Natural

Manifold Adjustment Procedure:

1 − Connect a test gauge to outlet pressure tap on gas

valve. Start unit and allow 5 minutes for unit to reach
steady state.

2 − While waiting for the unit to stabilize, notice the flame.

Flame should be stable and should not lift from burner.
Natural gas should burn blue. L.P. gas should burn
mostly blue with some orange streaks.

3 − After allowing unit to stabilize for 5 minutes, record

manifold pressure and compare to values given in
table 9.

NOTE−Shut unit off and remove manometer as soon as
an accurate reading has been obtained. Take care to
replace pressure tap plug.

F− Proper Gas Flow (Approximate)

Furnace should operate at least 5 minutes before check­ing gas flow. Determine time in seconds for two revolu­tions of gas through the meter. (Two revolutions assures
a more accurate time.) Divide by two and compare to
time in table 10 below. Adjust manifold pressure on gas
valve to match time needed.

NOTE− To obtain accurate reading, shut off all other
gas appliances connected to meter.

TABLE 10

GAS METER CLOCKING CHART

Seconds for One Revolution

80UHG

Unit

−45 80 160 200 400

−60 60 120 150 300

−100 36 72 90 180

−120 30 60 75 150

Natural−1000 btu/cu ft LP−2500 btu/cu ft

Natural LP

1 cu ft

Dial

2 cu ft

Dial

1 cu ft

Dial

2 cu ft

DIAL

To Measure Flame Signal − Ignition Control:

A transducer (Part
#78H5401 available from
Lennox Repair Parts) is

TRANSDUCER

(PART #78H5401)

required to measure
flame signal if meter used
will not read a low micro
amp signal. Seefig­ure21. The transducer

FIGURE 21

converts microamps to volts on a 1:1 conversion. Flame sig­nal should for the EGC control should be 1.0 − 5.0 with a lock−
out signal of .45 nominal microamps, therefore a reading of

1.0 − 5.0 nominal volts should be read on the meter. Flame
signal for the SureLight control should read 0.7 microamps
with a lockout signal of .15 microamps. A digital readout meter
must be used. The transducer plugs into most meters.
See figure 22 for proper use of transducer.

1 − Set the volt meter to the DC voltage scale. Insert

transducer into the VDC and common inputs. Ob­serve correct polarities. Failure to do so results in

negative (−) values.
2 − Turn off supply voltage to control.
3 − Disconnect ignition control flame sensor wire from the

flame sensor.
4 − Connect (−) lead of the transducer to flame sensor.
5 − Connect (+) lead of transducer to the ignition control sen-

sor wire.
6 − Turn supply voltage on and close thermostat contacts to

cycle system.
7 − When main burners are in operation for two minutes, take

reading. Remember 1 DC volt = 1 DC microamp.

NOTE−MUST USE DIGITAL METER

IMPORTANT

For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.

G−Flame Signal

A microamp DC meter is needed to check the flame signal
on the ignition control.

Flame (microamp) signal is an electrical current which passes
from the furnace control through the sensor during unit opera­tion. Current passes from the sensor through the flame to
ground to complete a safety circuit.

Page 17

(+) TO

IGNITION

CONTROL

SENSOR

WIRE

SET DIAL TO MEASURE VDC

RED COLLAR

(+)

(−)

(−) TO

FLAME SENSOR

INDICATES

POSITIVE

FIGURE 22

LEAD

WARNING

Fire and explosion hazard.
These instructions MUST be followed exactly.
Can cause a fire or explosion resulting in property

damage, personal injury or loss of life.

V−TYPICAL OPERATING CHARACTERISTICS
A−Blower Operation and Adjustment

NOTE− The following is a generalized procedure and
does not apply to all thermostat controls.

1 − Blower operation is dependent on thermostat control

system.

2 − Generally, blower operation is set at thermostat sub-

base fan switch. With fan switch in ON position, blower
operates continuously on heating speed. With fan
switch in AUTO position, blower cycles with demand or
runs continuously while heating or cooling circuit cycles.

3 − Depending on the type of indoor thermostat, blower

and entire unit will be off when the system switch is in
OFF position.

B−Temperature Rise

Temperature rise for 80UHG units depends on unit input,
blower speed, blower horsepower and static pressure as
marked on the unit rating plate. The blower speed must be
set for unit operation within the range of AIR TEMP. RISE
°F" listed on the unit rating plate.

To Measure Temperature Rise:

1 − Place plenum thermometers in the supply and return

air plenums. Locate supply air thermometer in the first
horizontal run of the plenum where it will not pick up ra-

diant heat from the heat exchanger.
2 − Set thermostat to highest setting.
3 − After plenum thermometers have reached their high-

est and steadiest readings, subtract the two readings.

The difference should be in the range listed on the unit

rating plate. If the temperature is too low, decrease

blower speed. If temperature is too high, first check

the firing rate. Provided the firing rate is acceptable, in-

crease blower speed to reduce temperature. To

change blower speed taps see the Blower Speed Taps

section in this manual.

C−External Static Pressure

1 − Tap locations shown in figure 23.
2 − Punch a 1/4" diameter hole

in supply and return air ple­nums. Insert manometer
hose flush with inside edge
of hole or insulation. Seal
around the hose with per­magum. Connect the zero
end of the manometer to the
discharge (supply) side of the system. On ducted sys­tems, connect the other end of manometer to the re­turn duct as above. For systems with non−ducted re­turns, leave the other end of the manometer open to
the atmosphere.

3 − With only the blower motor running and the evaporator

coil dry, observe the manometer reading. Adjust blow­er motor speed to deliver the air desired according to
the job requirements.

4 − External static pressure drop must not be more than

0.5" W.C.

5 − Seal around the hole when the check is complete.

STATIC PRESSURE

TEST

MANOMETER

80UHG UNIT

FIGURE 23

D−Blower Speed Taps Leadless Motors

80UHG−1 Models

Blower speed tap selection is accomplished by changing the
taps at the blower motor harness connector. Disconnect har­ness connector from motor to expose speed selectors.
Blower speed selections are listed in table 11.
To Change Blower Speed:
1 − Turn off electric power to furnace.
2 − Remove blower access door.

Disconnect blower motor harness from motor.

3 − Select desired speeds for heating and cooling. (Red =

heating, Black = cooling, White = common).

4 − Depress harness connector tab to release wire termi-

nal. Select connector location for new speed (refer to
unit wiring diagram). Insert wire terminal until it is se­curely in place. See figure 24.

5 − Replace harness connector to motor.

TABLE 11

Page 18

BLOWER SPEED TAP SELEC-

TION

Leaded Motors

DEPRESS TAB TO RELEASE
WIRE TERMINAL. SELECT
CONNECTOR LOCATION
FOR NEW SPEED (REFER TO
UNIT WIRING DIAGRAM). IN­SERT WIRE UNTIL IT IS SE­CURELY IN PLACE.

HARNESS

CONNECTOR

MOTOR

FIGURE 24

E−Blower Speed Taps Leaded Motors

80UHG−2 Models

Blower speed tap changes are made on the SureLight
control board. See figure 6. Unused taps must be secured
on two dummy terminals labeled "PARK on the SureLight
board. The heating tap is connected to the "HEAT−H " ter­minal and the cooling tap is connected to the "COOL−H"
terminal. The continuous blower tap is the same as the
heating tap.
To change existing heat tap, turn off power then switch out
speed tap on "HEAT−H" with tap connected to "PARK" .
See table 12 for blower motor tap colors for each speed.

TABLE 12

VI−MAINTENANCE

At the beginning of each heating season, the system
should be checked as follows:

A−Filters

Return air filter is not supplied with unit. See Optional Ac­cessaries section in this manual for filter and rack size. A
filter must be used in order to ensure long life and proper
operation. The filter is located in the return air duct or return
air register. Filters must be cleaned or replaced when dirty
to assure proper unit operation.

B− Heat Exchanger and Burners

Due to dimples designed in the heat exchanger, cleaning
is not recommended. Removal is for inspection only.

NOTE−Use papers or protective covering in front of fur­nace while cleaning furnace.

To clean burners:

1 − Remove screws holding upper burner mounting rail (fig-

ure 17). Remove rail.

2 − Slide burners off each orifice pull burners from heat ex-

changer.

3 − Clean holes in burner head (retention ring) with a wire

brush. See figure 17.

4 − With a shop vacuum or rags, clean out soot and scale

deposits from burners.

5 − Remove screws securing flue box to vestibule panel.

Remove flue box from unit. Leave combustion air
blower attached to flue box.

6 − With a shop vacuum or rags, clean out soot and scale

deposits from heat exchanger tubes and flue box. If tur­bulators are removed (figure 1) make sure they are re­installed before reassembling units.

7 − Inspect heat exchanger for corrosion damage, holes or

cracks.

8 − Replace burners making sure to fully engage on orifice.

Resecure burner mounting rail and flue box. Inspect flue
box gasket. Replace gasket if necessary.

9 − Slide heat exchanger into cabinet and re-secure heat

exchanger screws.

10 − Reinstall filler piece making sure that there is a good

seal between the cabinet sides, blower and deck and
filler piece. Use silicon caulking to fill in any potential

gaps.
11 − Re-secure flue pipe, gas piping and access panels.
12 − Carefully check all piping connections (factory and

field) for gas leaks. Use a leak detecting solution or oth-

er preferred means.
12 − Turn on gas and electrical supply.

Page 19

HEAT EXCHANGER REMOVAL (unit shown in horizontal position)

REMOVE SCREWS (4)

SLIDE ENTIRE ASSEMBLY OUT OF CABINET

FIGURE 25

CAUTION

Potential for gas leaks, fire or explosion.
Some soaps used for leak detection are corrosive
to certain metals. Carefully clean piping thor­oughly after leak detection has been completed.
Can cause damage to piping resulting in gas
leaks, fire or explosion.

C−Supply Air Blower

1 − Check and clean blower wheel.
2 − Motors used on the Lennox 80UHG series units are

permanently lubricated and need no further lu­brication.

Left

Back

Bottom

Front

Right

To p

D−Flue and Chimney

Flue must conform to all AGA/GAMA venting require­ments. Flue pipe deteriorates from the inside out and must
be disconnected in order to check thoroughly. Check flue
pipe, chimney and all connections for tightness and to
make sure there is no blockage or leaks.

E−Electrical

1 − Check all wiring for loose connections.
2 − Check for correct voltage.
3 − Check amp−draw on blower motor.

Page 20

VII− Wiring and Sequence of Operation

80UHG−1 MODEL WITH EGC CONTROL (SEE FLOW CHARTS ON THE FOLLOWING TWO PAGES):

1 − When disconnect is closed, 120V is routed through door

interlock switch (S51) to feed the line voltage side of the
ignition control (A3) and transformer T1 primary. Door in­terlock switch must be closed for A3 and T1 to receive
voltage.

2 − T1 supplies 24VAC to terminal 24VAC" on A3. In turn,

terminal R" of A3 supplies 24VAC to terminal R" of the
indoor thermostat (not shown).

3 − When there is a call for heat, W1 of the thermostat en-

ergizes W of the ignition control with 24VAC.

4 − CAB of the ignition control energizes the combustion air

inducer (B6). When the combustion air inducer
nears full speed, combustion air prove switch (S18)
closes. Switch must close within 2 1/2 minutes or
control goes into 5 minute Watchguard Pressure
Switch delay.

5 − When S18 closes, assuming primary limit (S10) and

secondary limit (S21) are closed, a 15 second pre−purge
begins. After the pre−purge period the ignition control
starts ignition spark and opens main gas valve.

6 − After 45 seconds, ignition control (A3) energizes the

indoor blower (B3).

7 − When heat demand is satisfied, W1 of the thermostat de-

energizes W of the ignition control and the gas valve is
immediately de-energized. The combustion air inducer
immediately stops. The indoor blower runs for a desig­nated fan off" period (60−240 seconds) as set by jumper
on ignition control.

Page 21

80UHG−1 HEATING SEQUENCE OF OPERATION

NORMAL HEATING MODE

CONTROL MAIN POWER ON"

FLAME OFF?

YES

CONTROL SELF−CHECK OKAY?

YES

ROLL−OUT SWITCH CLOSED

YES

LED: SLOW FLASH RATE

THERMOSTAT CALLS FOR HEAT

LED: FAST FLASH RATE

COMB. AIR INDUCER PRESSURE SWITCH OPEN?

YES

COMBUSTION AIR INDUCER ON?

HTG ACC. TERM. ENERGIZED?

YES

PRESSURE SWITCH CLOSED WITHIN 2.5 MIN.?

YES

COMB. AIR INDUCER PREPURGE (15 seconds)

IGNITION TRIAL (10 seconds) −− START IGNITION

SPARK, OPEN MAIN GAS VALVE.

NO

NO

NO

NO

NO

ABNORMAL HEATING MODE

GAS VALVE OFF. COMB. INDUCER ON. INDOOR

BLOWER ON HEAT SPEED. SEQUENCE HOLDS UNTIL

NO FLAME SENSED OR MAIN POWER IS INTERRUPTED

AND RESET. DIAG. CODE: 1− FLASHING; 2−OFF

(FLAME SENSED WITHOUT VALVE ENERGIZED)

GAS VALVE, COMB. INDUCER AND INDOOR BLOWER

(WITH DELAY) OFF. REMOVE POWER TO RESET

CONTROL. DIAG. CODE: BOTH ON (CONTROL

SELF−CHECK FAILURE OR INCORRECT WIRING)

GAS VALVE, COMB. BLOWER AND INDOOR BLOWER

(WITH DELAY) OFF. SEQUENCE HOLDS UNTIL

ROLL−OUT SWITCH IS MANUALLY CLOSED.

2−FLASHING (FLAME ROLL−OUT OPEN)

GAS VALVE, COMB. INDUCER AND INDOOR BLOWER

(WITH DELAY) OFF. SEQUENCE HOLDS UNTIL

PRESSURE SWITCH CLOSES OR THERMOSTAT

RESETS CONTROL. DIAG. CODE: 1−OFF;

2−FLASHING (C.A.B. PRESSURE SWITCH OPEN)

YES

PRESSURE SWITCH WATCHGUARD CONDITION:

GAS VALVE, COMB. INDUCER AND INDOOR BLOWER

(WITH DELAY) OFF. DIAG. CODE: 1−OFF /

2−FLASHING (C.A.B. PRESSURE SWITCH OPEN) IS 5

MINUTE RESET PERIOD COMPLETE?

DIAG. CODE: 1−ON;

HAS FLAME REGISTERED WITHIN 10 SECONDS

AFTER IGNITION TRIAL?

YES

IS FLAME SENSED AFTER 10 SECOND

FLAME RECTIFICATION PERIOD?

YES

INDOOR AIR BLOWER ON.

(Fixed 45−second delay)

PRIMARY/SECONDARY LIMITS MONITORED IN

HEAT CYCLE. ARE SWITCHES CLOSED?

YES

PRESSURE SWITCH CLOSED?

YES

THERMOSTAT OPENS

LED: SLOW FLASH RATE

COMB. AIR INDUCER OFF (5 sec. delay)

HTG ACC. TERM. DE−ENERGIZED.

INDOOR AIR BLOWER OFF (After selected 60, 90,

120, 180, or 240 delay)?

NO

NO

NO

NO

GAS VALVE OFF. COMB. INDUCER ON. INDOOR

BLOWER (WITH 45 DELAY) ON. HAS CONTROL FAILED

FLAME SENSE 5 TIMES DURING ONE HEAT DEMAND?

IF YES, SYSTEM GOES INTO 60 MIN.WATCHGUARD.

DIAG. CODE: 1−ALT. FLASHING / 2−ALT. FLASHING IF

NO, GO TO COMB. AIR BLOWER ON?"

HAS CONTROL RESET IGNITION SEQUENCE 5 TIMES

IF YES, SYSTEM GOES INTO 60 MIN. WATCHGUARD.
DIAG. CODE: 1−ALT. FLASHING / 2−ALT. FLASHING IF

NO, GO TO COMB. AIR BLOWER ON?"

GAS VALVE OFF. COMB. INDUCER OFF. INDOOR

BLOWER ON UNTIL LIMIT CLOSES. DIAG.

CODE: 1−FLASHING / 2−ON (LIMIT OPEN)

IS LIMIT NOW CLOSED?

YES

HAS PRIMARY LIMIT OPENED 5 TIMES DURING

ONE UNSATISFIED HEAT DEMAND. IF YES,

SYSTEM GOES INTO 60 MIN.WATCHGUARD.

DIAG. CODE: 1−FLASHING / 2−ON

IF NO, GO TO COMB. AIR BLOWER ON?"

GAS VALVE, COMB. INDUCER AND INDOOR BLOWER

(WITH DELAY) OFF. DIAG. CODE: 1−OFF / 2−FLASHING

(C.A.B. PRESSURE SWITCH OPEN) HAS C.A.B.

PRESSURE SWITCH CLOSED IN 2.5 MINUTES?

YES

NO

Page 22

80UHG−1 COOLING SEQUENCE OF OPERATION

REMAINS UNCHANGED THROUGHOUT COOLING CYCLE.

THERMOSTAT CALLS FOR COOLING.

COMPRESSOR CONTACTOR AND SYSTEM FAN

ENERGIZED AT COOLING SPEED AFTER

1 SECOND DELAY. ACC TERMINAL ENERGIZED.

SYSTEM FAN AND ACC TERMINAL OFF AFTER

LED: Slow flash rate.

THERMOSTAT OPENS.

COMPRESSOR OFF.

0 SECONDS.

80UHG−1 MANUAL CONTINUOUS FAN SEQUENCE OF OPERATION

REMAINS UNCHANGED THROUGHOUT SEQUENCE.

CONTINUOUS FAN SELECTION MADE AT THERMOSTAT.

CONTROL ENERGIZES SYSTEM FAN AT HEATING SPEED.

LED: Slow flash rate.

ACC TERMINAL ENERGIZED.

THERMOSTAT CALLS FOR COOLING.

YES NO

SYSTEM FAN SWITCHED TO COOLING

SPEED. ACC TERMINAL REMAINS ENERGIZED.

THERMOSTAT OPENS.

SYSTEM FAN SWITCHES TO HEATING SPEED

AND ENERGIZES ACC TERMINAL. BOTH REMAIN ON

UNTIL CONTINUOUS FAN IS SWITCHED OFF AT THERMOSTAT.

THERMOSTAT CALLS FOR HEAT.

NO

YES

SYSTEM FAN REMAINS ON HEATING SPEED AFTER

SELECTED DELAY. ACC TERM. REMAINS ENERGIZED.

HTG ACC. TERM. ENER-

GIZED WITH COMB. AIR IN-

DUCER

THERMOSTAT OPENS.

SYSTEM FAN SWITCHED OFF AFTER DELAY.

ACC TERMINAL DE−ENERGIZED.

Page 23

80UHG−2 MODEL WITH SURELIGHT CONTROL

1 − When there is a call for heat, W1 of the thermostat en-

ergizes W of the furnace control with 24VAC.

2 − S10 primary limit switch and S47 rollout switch are

closed. Call for heat can continue.

3 − SureLight control energizes combustion air blower

B6. Combustion air inducer runs until S18 combus­tion air prove switch closes (switch must close within
2−1/2 minutes or control goes into 5 minute Watch­guard Pressure Switch delay). Once S18 closes, a
15−second pre−purge follows.

4 − SureLight control energizes ignitor. A 20−second

warm−up period begins.

5 − Gas valve opens for a 4−second trial for ignition (igni-

tor will remain energized for the first second).

6 − Flame is sensed, gas valve remains open for the heat

call.

7 − After 45−second delay, SureLight control energizes

indoor blower B3.

8 − When heat demand is satisfied, W1 of the indoor ther-

mostat de−energizes W of the SureLight control which
de−energizes the gas valve. Combustion air inducer
B6 continues a 5−second post−purge period, and in­door blower B3 completes a selected OFF time delay.

Page 24

HEATING SEQUENCE OF OPERATION

NO

NORMAL HEATING MODE

POWER ON

CONTROL SELF−CHECK OKAY?

YES

IS POLARITY REVERSED?

NO

NO

IS VOLTAGE

ABOVE 75 VOLTS?

YES

ROLLOUT SWITCH CLOSED?

YES

BURNER OFF?

(CONTINUOUS FLAME CHECK)

YES

NORMAL OPERATION:

LED #1 −− SLOW FLASH
LED #2 −− SLOW FLASH

YES

THERMOSTAT CALLS FOR HEAT:

LED #1 −− FAST FLASH
LED #2 −− FAST FLASH

YES

PRIMARY AND SECONDARY LIMIT SWITCH.

CLOSED?

YES

IS COMBUSTION AIR

PRESSURE SWITCH OPEN?

YES

IS COMBUSTION AIR BLOWER

ENERGIZED?

YES

HAS COMBUSTION AIR PRESSURE
SWITCH CLOSED IN 2.5 MINUTES?

YES

ABNORMAL HEATING MODE

GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.

NO

YES

NO

NO

NO

(RESET CONTROL BY TURNING MAIN POWER OFF.)

THERMOSTAT. CONTROL WILL NOT RESPOND

UNTIL VOLTAGE RISES ABOVE 75 VOLTS.

GAS VALVE OFF. COMBUSTION AIR INDUCER ON.

SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES.

GAS VALVE OFF. COMBUSTION AIR INDUCER ON.

NO

NO

PRESSURE SWITCH IS IN WATCHGUARD MODE.

GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.

IS 5-MINUTE RESET PERIOD COMPLETE?

INDOOR BLOWER DELAY OFF.

LED #1 ON
LED #2 ON

POLARITY REVERSED.

LED #1 −− FAST FLASH

LED #2 −− SLOW FLASH

LED SIGNALS WAITING ON CALL FROM

INDOOR BLOWER ON.

LED #1 −− ON. LED #2 −− SLOW FLASH.

INDOOR BLOWER ON HEATING SPEED.

LED #1 −− SLOW FLASH

LED #2 −− OFF

COMBUSTION AIR INDUCER OFF.

INDOOR BLOWER ON

LED #1 SLOW FLASH RATE

LED #2 −− ON

GAS VALVE OFF.

COMBUSTION AIR INDUCER OFF.

INDOOR BLOWER OFF WITH DELAY.

LED #1 OFF

LED #2 SLOW FLASH

(Sequence holds until pressure switch

closes or thermostat resets control.)

INDOOR BLOWER OFF WITH DELAY.

LED #1 −− OFF. LED #2 −− SLOW FLASH.

CONTINUED NEXT PAGE

Page 25

HEATING SEQUENCE CONTINUED

NORMAL HEATING MODE ABNORMAL HEATING MODE

15-SECOND COMBUSTION AIR INDUCER PREPURGE

INITIATED BY CLOSED PRESSURE SWITCH.

YES

IGNITOR WARM-UP −− 20 SECONDS.

YES

4-SECOND TRIAL FOR IGNITION.

GAS VALVE OPENS. IGNITOR ENERGIZED FOR 1

SECOND AFTER VALVE OPENS. CONTROL

10M9301: IGNITOR ENERGIZED DURING TRIAL

UNTIL FLAME SENSED.

YES

FLAME STABILIZATION PERIOD.

4 SECONDS

FLAME RECTIFICATION CURRENT

CHECK. CAN FLAME BE PROVEN WITHIN

4 SECONDS AFTER GAS VALVE OPENS?

(u0.15 microamps)

YES

FLAME PRESENT?

YES

FLAME SIGNAL ABOVE 0.2 MICROAMPS?

YES

INDOOR BLOWER ON DELAY BEGINS

(45 seconds.)

YES

PRIMARY AND SECONDARY LIMIT

SWITCHES CLOSED?

YES

IS VOLTAGE ABOVE 75 VOLTS?

NO

IS THERE A PROPER GROUND?

YES

IS IGNITOR INTACT AND CONNECTED?

GAS VALVE OFF. COMBUSTION AIR INDUCER ON.

NO

HAS CONTROL FAILED TO SENSE FLAME FOR

FIVE CONSECUTIVE TRIES DURING A SINGLE

LEDs SIGNAL WATCHGUARD FAILURE CODE.

IS 60-MINUTE RESET PERIOD COMPLETE?

NO

NO

(Does not affect operation of control)

COMBUSTION AIR INDUCER DE−ENERGIZED.

INDOOR BLOWER ON UNTIL SWITCH CLOSES.

NO

LED #1 −− SLOW FLASH. LED #2 −− ON.

YES

YES

INDOOR BLOWER OFF.

HEAT DEMAND?

WATCHGUARD MODE. GAS VALVE OFF.

COMBUSTION AIR INDUCER OFF.

INDOOR BLOWER OFF WITH DELAY

HAS CONTROL RESET IGNITION

SEQUENCE FOUR TIMES?

LOW FLAME SIGNAL

LED #1 −− SLOW FLASH

LED #2 −− FAST FLASH

GAS VALVE DE−ENERGIZED.

IS LIMIT SWITCH CLOSED?

YES

HAS PRIMARY SECONDARY

LIMIT RESET (CLOSED)

WITHIN 3 MINUTES?

NO

NO

LEDS SIGNAL

ALTERNATING

FAST FLASH

NO

YES

LIMIT SWITCH

WATCHGUARD

MODE. GAS VALVE

OFF. COMB. AIR

INDUCER OFF.
INDOOR BLOWER
OFF WITH DELAY.

LED#1−SLOW

FLASH LED#2− ON.

IS 60−MINUTE

RESET PERIOD

COMPLETE?

NO

YES

NO

YES

NO

ROLLOUT SWITCH CLOSED?

YES

COMBUSTION AIR PRESSURE

SWITCH CLOSED?

YES

THERMOSTAT DEMAND SATISFIED.

YES

LED #1 & #2 SIMULTANEOUS SLOW FLASHES.

YES

COMB. AIR INDUCER CONTINUES 5-SECOND

POST PURGE AFTER T’STAT DEMAND IS SATISFIED.

INDOOR AIR BLOWER COMPLETES SELECTED

OFF" DELAY BEFORE SHUTTING OFF.

NO

SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET

NO

THERMOSTAT IS CYCLED OFF/ON FOR 1 TO 20 SEC.

GAS VALVE DE−ENERGIZED.

COMBUSTION AIR INDUCER ON.

INDOOR BLOWER OFF WITH DELAY

LED #1 −− OFF. LED #2 −− SLOW FLASH.

HAS CAB SWITCH CLOSED IN 2.5 MINUTES?

5-MINUTE PRESSURE SWITCH

GAS VALVE POWER OFF.

COMBUSTION AIR INDUCER POWER ON.

INDOOR BLOWER ON

LED #1 −− ON. LED #2 −− SLOW FLASH.

AND MAIN POWER IS INTERUPTED OR

NO

WATCHGUARD MODE.

Page 26

YES

COOLING SEQUENCE OF OPERATION

NORMAL COOLING MODE ABNORMAL COOLING MODE

POWER ON

IGNITION CONTROL MAIN POWER ON.

CONTROL SELF DIAGNOSTIC CHECK.

IS CONTROL OPERATING NORMALLY?

YES

IS POLARITY REVERSED?

NO

IS VOLTAGE

ABOVE 75 VOLTS?

YES

ROLLOUT SWITCH MONITORED CONTINUOUSLY.

IS ROLLOUT SWITCH CLOSED?

YES

CHECK FOR MAIN BURNER FLAME SENSE.

IS MAIN BURNER FLAME OFF?

YES

LED: SLOW FLASH RATE REMAINS UNCHANGED

THROUGHOUT COOLING CYCLE.

THERMOSTAT CALLS FOR COOLING.

NO

NO

YES

NO

NO

GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.

INDOOR BLOWER OFF WITH NORMAL DELAY.

SIGNAL CIRCUIT BOARD FAILURE AT LED.

INTERRUPT MAIN POWER TO RESET CONTROL.

SIGNAL POLARITY REVERSED AT LED.

LED SIGNALS WAITING ON CALL FROM

THERMOSTAT. CONTROL WILL NOT RESPOND

UNTIL VOLTAGE RISES ABOVE 75 VOLTS.

GAS VALVE OFF. COMBUSTION AIR INDUCER ON.

INDOOR BLOWER ON.

SIGNAL ROLL-OUT SWITCH OPEN AT LED.

SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES.

GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.

INDOOR BLOWER OFF WITH NORMAL DELAY.

SIGNAL UNWANTED FLAME SENSED AT LED.

SEQUENCE HOLDS UNTIL FLAME IS NOT SENSED.

COMPRESSOR CONTACTOR AND SYSTEM FAN

ENERGIZED WITH 0-SECOND DELAY

(COOLING SPEED). EAC−H TERM. ENERGIZED.

THERMOSTAT OPENS.

COMPRESSOR OFF.

SYSTEM FAN AND ACC. TERM. OFF

WITH 0-SECOND DELAY.

Page 27

SURELIGHT CONTROL

CONTINUOUS HEAT SPEED FAN SEQUENCE OF OPERATION

LED: SLOW FLASH RATE REMAINS

UNCHANGED THROUGHOUT SEQUENCE.

MANUAL FAN SELECTION MADE AT THERMOSTAT.

CONTROL (G) ENERGIZES SYSTEM FAN AT HEAT−H

HEAT SPEED. EAC−H TERMINAL IS ENERGIZED.

THERMOSTAT CALLS FOR HEAT (W).

NO

THERMOSTAT CALLS FOR COOLING.

YES

SYSTEM FAN SWITCHED TO COOL−H SPEED.

EAC−H TERM. REMAINS ON.

THERMOSTAT OPENS.

MANUAL FAN SELECTION MADE AT THERMOSTAT.

CONTROL (G) ENERGIZES SYSTEM FAN AT HEAT−H

HEAT SPEED. EAC−H TERM. ENERGIZED.

HUM−N TERM. ENERGIZES

WITH COMB. AIR BLOWER.

YES

SYSTEM FAN REMAINS ON HEAT−H

HEATING SPEED.

THERMOSTAT OPENS.

NO

HUM−N TERM. DE−ENERGIZES

WITH COMB. AIR INDUCER

SYSTEM FAN REMAINS ON HEAT−H

HEATING SPEED.

Page 28

VIII−Troubleshooting−SureLight Control

code

code
LED#2−Sl

h

ACTION 1

ducer does not energize

ducer does not energize

120V field connection

on operation

SURELIGHT − TROUBLE SHOOTING GUIDE

UPON INITIAL POWER UP, REMOVE ALL THERMOSTAT DEMANDS TO THE UNIT

PROBLEM: 1 UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE

Condition Possible Cause Corrective Action / Comments

1.1

− Both diagnostic lights fail to light up.

LED#1−Off
LED#2−Off

1.2

− Diagnostic lights flash the roll−out

.

.

LED#1−On,

ow Flas

1.3

− On initial power−up the comb. air in­.

.

− Diagnostic lights flash the reverse

polarity code.

Main voltage 120V not supplied to
unit.

Miswiring of furnace or improper
connections.

Door interlock switch failure.

Transformer Failure.

Failed control board.

Roll−out switch open.

Roll−out switch failure.

Miswiring or improper connections at
roll−out switch.

12 pin connector failure

120V main power polarity reversed.

1.1.1

1.1.2

1.1.3

Blown fuse

1.1.4

1.1.5

1.1.6

1.2.1

1.2.2

1.2.3

1.2.4

1.3.1

ACTION 1 − Check 120V main voltage.

Determine cause of main power failure.

ACTION 1 − Check for correct wiring of 120V to
power make up box and transformer.

ACTION 2 − Check 24V wiring to control board.

ACTION 1 − Replace fuse.
ACTION 2 − If fuse still blows, check for short.

ACTION 1 − Check that door switch is activated

when door is closed.
ACTION 2 − Check wire connections to switch, re­place loose connectors.
ACTION 3 − Check continuity of switch in closed
position. Replace if defective.

ACTION 1 − Check that transformer output is
24V. Replace if defective.

ACTION 1 − If all the above items have been
checked, replace board.

ACTION 1 − Manually reset the roll−out switch
by pushing the top button.
ACTION 2 − Determine the cause of the roll−out
switch activation before leaving furnace.

ACTION 1 − Check continuity across roll−out
switch. Replace roll−out switch if switch is reset
but does not have continuity.

− Check wiring connections to switch.

ACTION 1 − Check 12−pin connector for proper

connection to control board.
ACTION 2 − Check continuity of the multi plug
pin.

ACTION 1 − Check the 120V has line and neutral
correctly input into control.
ACTION 2 − Reverse the line and neutral at the
120V field connection.

.

LED#1−Fast Flash,
LED#2−Slow Flash.

1.4

− On initial power up the combustion

air inducer does not energize.

− Diagnostic lights flash normal power

on operation.

.

LED#1−Slow Flash
LED#2−Slow Flash

1.4.1

Open combustion air inducer motor
circuit.

1.4.2

Failed combustion air inducer motor.

Page 29

ACTION 1 − Check for 120V to combustion air
inducer. If no power, check wire and connec­tions.

ACTION 1 − If power is present at blower, replace
blower.

PROBLEM 1: UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE

g

LED#2 Alternating Fast Flash

gg

Diagnostic lights flash the pressure

Condition Possible Cause Corrective Action / Comments

1.5

− Diagnostic lights flash the improper

main ground.

LED#1−Alternating Fast Flash
LED#2−Alternating Fast Flash

1.5.1

Improper ground to the unit.

1.5.2

4−Pin connector is improperly at-

tached to the circuit board.

1.5.3

Line voltage is below 75V.

1.5.4

Open ignitor circuit.

1.5.5

Broken or failed ignitor.

ACTION 1 − Check that the unit is properly
ground.
ACTION 2 − Install a proper main ground to the
unit

ACTION 1 − Check 4−pin connector for proper
installation. Correctly insert connector into con­trol.

ACTION 1 − Check that the line voltage is above
75V. Determine cause of voltage drop and sup­ply correct voltage to the control.

ACTION 1 − Check for correct wiring and loose
connections in the ignitor circuit. Check mult−
plug connections for correct installation.

ACTION 1 − Unplug ignitor and read resistance
across ignitor. If resistance does not read be­tween 10.9 and 19.7 ohms, replace the ignitor.

PROBLEM 2: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES

NOT ENERGIZE

Condition Possible Cause Corrective Action / Comments

2.1

− Unit operates with a cooling or con-

tinuous fan demand.

− Combustion air inducer will not start

with a Heating demand.

− Diagnostic lights flash the limit failure

mode.

LED#1−Slow Flash,
LED#2−On

2.1.1

Primary or secondary (if equipped )

limit open.

2.1.2

Miswiring of furnace or improper con-

nections at limit switch(es).

ACTION 1 − Check continuity across switch(es).
Switches reset automatically upon cool down.
ACTION 2 − Check for restrictions on blower inlet
air (including filter) and outlet air. Determine
cause for limit activation before placing unit back
in operation.

ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.

2.2

− Unit operates with a cooling and con-

tinuous fan demand.

− Combustion air inducer will not start

with a Heating demand.

− Diagnostic lights flash the pressure

−

switch failure code.

LED#1−Off,
LED#2−Slow Flash

2.2.1

Miswiring of furnace or improper con-

nections to combustion air inducer.

2.2.2

Pressure switch stuck closed.

Page 30

ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.

ACTION 1 − Check that the pressure switch is
open without the combustion air inducer operat­ing. Replace if defective.

PROBLEM 2: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR INDUCER DOES

g

LED#1 Off

NOT ENERGIZE (CONT.).

Condition Possible Cause Corrective Action/Comments

2.3

− Unit operates with a cooling and con-

tinuous fan demand.

− Combustion air inducer will not start

with a Heating demand.

Miswiring of furnace or improper con-

nections to combustion air inducer.

2.3.1

ACTION 1 − Check for correct wiring and loose

connections. Correct wiring and/or replace any
loose connections.

− Diagnostic lights flash the pressure

switch failure code 2.5 minutes after
heating demand.

ACTION 1 − If there is 120V to combustion air in­ducer and it does not operate, replace combus­tion air inducer.

LED#1−Off,

2.3.2

Combustion air inducer failure.

LED#2−Slow Flash

PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER

ENERGIZES, IGNITOR IS NOT ENERGIZED.

Condition Possible Cause Corrective Action/Comments

3.1

− Unit operates with a cooling and

continuous fan demand.

− Combustion air inducer energizes

with a heating demand.

− Diagnostic lights flash the pressure

switch failure code 2.5 minutes after
heating demand.

LED#1−Off
LED#2−Slow Flash

Pressure switch does not close due

to incorrect routing of the pressure

Pressure switch does not close due

to obstructions in the pressure lines.

Pressure switch lines damaged

Condensate in pressure switch line.

Pressure switchdoes not close due to

a low differential pressure across the

Wrong pressure switch installed in

the unit, or pressure switch is out of

Miswiring of furnace or improper con-

nections at pressure switch.

Pressure switch failure.

3.1.1

switch lines.

3.1.2

3.1.3

3.1.4

3.1.5

pressure switch.

3.1.6

calibration.

3.1.7

3.1.8

ACTION 1 − Check that the pressure switch lines

are correctly routed. Correctly route pressure
switch lines.

ACTION 1 − Remove any obstructions from the
the pressure lines and/or taps.

ACTION 1 − Check pressure switch lines for
leaks. Replace any broken lines.

ACTION 1 − Check pressure switch lines for con­densate. Remove condensate from lines. Check
that the condensate lines are located correctly.

ACTION 1 − Check the differential pressure
across the pressure switch. This pressure
should exceed the set point listed on the
switch.
ACTION 2 − Check for restricted inlet vent. Re­move all blockage.
ACTION 3 − Check for proper vent sizing and
run length. See installation instructions.

ACTION 1 − Check that the proper pressure
switch is installed in the unit. Replace pressure
switch if necessary.

ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.

ACTION 1 − If all the above modes of failure have
been checked, the pressure switch may have
failed. Replace pressure switch and determine if
unit will operate.

Page 31

PROBLEM 4: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER

ignite code.

ENERGIZES, IGNITOR IS ENERGIZED.

Condition Possible Cause Corrective Action/Comments

4.1

− Unit operates with a cooling and

continuous fan demand.

− Combustion air inducer energizes

with Heating demand.

− Ignitor is energized but unit fails to

light.

LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash

4.1.1

Check that gas is being supplied to

the unit.

4.1.2

Miswiring of gas valve or loose con-

nections at multi−pin control amp

plugs or valve.

4.1.3

Defective gas valve or ignition con-

trol.

ACTION 1 − Check line pressure at the gas
valve. Pressure should not exceed 13" WC for
both natural and propane. Line pressure should
read a minimum 4.5" WC for natural and 8.0"WC
for propane.

ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.

ACTION 1 − Check that 24V is supplied to the
gas valve approximately 35 seconds after heat
demand is initiated.
ACTION 2 − Replace the valve if 24V is supplied
but valve does not open.
ACTION 3 − Replace the control board if 24V is
not supplied to valve.

PROBLEM 5: BURNERS LIGHT WITH A HEATING DEMAND BUT UNIT SHUTS DOWN

PREMATURELY

Condition Possible Cause Corrective Action/Comments

5.1

− Burners fire with a heating de-

mand.

− Burners light but unit shuts off prior

to satisfying T−stat demand.

− Diagnostic lights flash the pressure

switch code.

5.1.1

Low pressure differential at the pres-

sure switch.

ACTION 1 − Check for restricted exhaust vent.
Remove all blockage.
ACTION 2: Check for proper vent sizing. See
installation instructions.

LED#1−Off
LED#2−Slow Flash

5.2

− Combustion air inducer energizes

with a heating demand.

− Burners light but fail to stay lit.

− After 5 tries the control diagnostics

flash the watchguard burners failed to
ignite code.

LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash

5.2.1

Sensor or sensor wire is improperly

installed.

5.2.2

Sensor or sensor wire is broken.

5.2.3

Sensor or sensor wire is grounded to

the unit.

5.2.4

Control does not sense flame.

ACTION 1 − Check that sensor is properly lo­cated and that the sense wire is properly at­tached to both the sensor and the control.

ACTION 1 − Check for a broken sensor.
ACTION 2 − Test continuity across the sense

wire. If wire or sensor are damaged replace
the component.

ACTION 1 − Check for resistance between the
sensor rod and the unit ground.
ACTION 2 − Check for resistance between the
sensor wire and the unit ground.

ACTION 3 − Correct any shorts found in circuit.

ACTION 1 − Check the microamp signal from

the burner flame. If the microamp signal is be­low 0.20 microamps, check the sensor rod for
proper location or contamination.
ACTION 2 − Replace, clean, or relocate flame
sensor rod. If rod is to be cleaned, use steel
wool or replace sensor. DO NOT CLEAN ROD
WITH SAND PAPER. SAND PAPER WILL
CONTRIBUTE TO THE CONTAMINATION
PROBLEM. NOTE: Do not attempt to bend
sensor rod.
ACTION 3 − Check that there is proper ground
to burner box. Repair as necessary.

Page 32

PROBLEM 5: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN

LED#1 On

Burners light roughly and the unit

Condition Possible Cause Corrective Action/Comments

5.3

− Combustion air inducer energizes

with a heating demand.

− Burners light.

− Roll−out switch trips during the

heating demand.

− Diagnostic lights flash roll−out fail-

ure.

LED#1−On
LED#2−Slow Flash

5.4

− Combustion air inducer energizes

with a heating demand.

− Burners light roughly and the unit

fails to stay lit.

− Diagnostic lights flash watchguard

flame failure.

PREMATURELY (CONT.)

5.3.1

Unit is firing above 100% of the

nameplate input.

5.3.2

Gas orifices leak at the manifold con-

nection.

5.3.3

Insufficient flow through the heat ex-

changer caused by a sooted or re-

stricted heat exchanger.

5.3.4

Burners are not properly located in

the burner box.

5.4.1

Poor Venting

5.4.2

Improper burner cross−overs

ACTION 1 − Check that the manifold pressure
matches value listed on nameplate. See installa­tion instructions for proper procedure.
ACTION 2 − Verify that the installed orifice size
match the size listed on the nameplate or instal­lation instructions.
ACTION 3 − Check the input rate to verify rate
matches value listed on nameplate.

ACTION 1 − Tighten orifice until leak is sealed.
NOTE: Be careful not to strip orifice threads.
ACTION 2 − Check for gas leakage at the

threaded orifice connection. Use approved
method for leak detection (see unit instructions).

ACTION 1 − Check for sooting deposits or other
restrictions in the heat exchanger assembly.
Clean assembly as outlined in instruction manu­al.
ACTION 2 − Check for proper combustion. See
NO TAG Heating System Service Checks sec­tion NO TAG.

ACTION 1 − Check that the burners are firing into
the center of the heat exchanger openings. Cor­rect the location of the burners if necessary.

ACTION 1 −Check vent pipe and remove any ob­structions
ACTION 2 − Check for correct exhaust vent
installation. See instructions

ACTION 1 − Remove burner and inspect the
cross−overs for burrs, or any restriction or if
crossover is warped. Remove restriction or re­place burners.

LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash

5.5

− Combustion air inducer energizes

with a heating demand.

− Burners light.

− Diagnostic lights flash watch guard

flame failure.

− NOTE" Unit might go into 60 min-

ute Watchguard mode depending on
intermittent nature of sensor signal.

LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash

5.4.3

Burrs in gas orifices

5.5.1

Loose sensor wire connection

causes intermittent loss of flame sig-

nal.

5.5.2

Poor ground to burner box

ACTION 1 − Remove gas orifices and inspect.
Remove any burrs that are present or replace
orifice.

ACTION 1 − Check that the sensor is properly lo­cated.
ACTION 2 − Check that the sense wire is proper­ly attached to both the sensor and the control.
Pay extra attention to the pin connectors.

ACTION 1 − Check for proper ground and repair
as necessary.

Page 33

PROBLEM 6: CONTROL SIGNALS LOW FLAME SENSE DURING HEATING MODE

sense code

Condition Possible Cause Corrective Action/Comments

6.0

− Unit operates correctly but the

diagnostic lights flash low flame

6.1.1

Sensor rod is improperly located on

the burner.

ACTION 1 − Check the sensor rod for proper
location on the burner. Properly locate the sen­sor rod or replace if rod cannot be located cor­rectly.

.

ACTION 1 − Check sensor rod for contamination
or coated surface. Clean the sensor rod with
steel wool or replace sensor. DO NOT USE
SAND PAPER TO CLEAN ROD. SAND PAPER
WILL CONTRIBUTE TO THE CONTAMI­NATION PROBLEM.

LED#1−Slow Flash
LED#2−Fast Flash

6.1.2

Sensor rod is contaminated.

PROBLEM 7: INDOOR BLOWER FAILS TO OPERATE IN COOLING, HEATING, OR CONTINUOUS

FAN MODE

Condition Possible Cause Corrective Action/Comments

7.0

− Indoor blower fails to operate in

continuous fan, cooling, or heating
mode.

Miswiring of furnace or improper con-

nections at control or indoor blower

120V is not being supplied to the in-

door air blower or blower motor fail-

Defective control board

7.1.1

motor.

7.1.2

ure.

7.1.3

7.1.4

ACTION 1− Correct wiring and/or replace any

loose connections. Check for correct wiring and
loose connections.

ACTION 1 − Check for 120V at the various calls
for indoor blower by energizing "Y", "G", and "W"
individually on the low voltage terminal strip.
Note that when "W’ is energized, the blower is
delayed 45 seconds. If there is 120V to each mo­tor tap but the blower does not operate, replace
the motor.

ACTION 1 − If there is not 120V when "Y", "G", or
"W" is energized, replace the control.

ACTION 1 − Replace capacitor

Defective run capacitor

PROBLEM 8: RF STATIC DURING TIME FOR IGNITION

Condition Possible Cause Corrective Action/Comments

8.0

− AM radio interference.

8.1.2

Ignitor operation

ACTION 1 − Call Technical Support, Dallas.

Page 34